CHECK FOR DISCUSSION POSTS AND COMMENTS IN THE EDIT TOOLBAR!

discussion posts ..........comments

=
Spotted knapweed is driving out native plants and destroying rangeland, costing ranchers millions. Can anybody stop this outlaw?

WAYNE SLAGHT is a rancher. He manages the 10,000 acre Two Creek Ranch in Powell County, Montana, the ranch he grew up on and that his father managed before him. It's in bear country, and he knows every grizzly that passes through this rolling patch of Big Sky country about 50 miles east of Missoula. It's elk country too, and one bitter November day he was pounding postholes in the frozen ground, erecting an eight-foot-high elk fence around a larder of hay that will feed his 800 cattle during the long winter that lies ahead. But the biggest threat to his livelihood doesn't even have teeth. "It's knapweed," he says without hesitation. Uncontrolled, "it could put me out of business in ten years as easily as a grizzly could take down one of my cows."

Spotted knapweed, as the plant is more formally known, is a national menace, a weed of mass destruction. In Montana alone, it covers some 4.5 million acres and costs ranchers more than $40 million annually in herbicide and lost productivity. Native from central Europe to Siberia, spotted knapweed reached North America in the late 19th century. It invades pastureland and renders huge tracts commercially useless, because cattle, horses and most other animals turn up their noses at it. The purple-flowered pest, which some nonranchers regard as beautiful, has become so rampant that elk have changed their migration routes to avoid it.

New research points to an unusual reason for the plant's success. Ragan Callaway of the University of Montana in Missoula, who studies how plants interact with one another, and Jorge Vivanco of Colorado State University have found that spotted knapweed conducts chemical warfare on its neighbors- the first comprehensive evidence of an invasive plant using an offensive chemical weapon.

Several thousand foreign plant and animal species, including zebra mussels from Eurasia and Asian long-horned beetles, have colonized the United States. About one in ten turns invasive, or spreads to such a degree that it disrupts existing ecosystems. All told, invasive species cost the nation upwards of $140 billion a year. But few rival spotted knapweed for sheer nastiness. It's "one of the worst invasive plant species in the United States, one that we really don't have much of a handle on yet," says Eric Lane, Colorado's weed coordinator.

SPOTTED KNAPWEED arrived in Victoria, British Columbia, in I883 either as a contaminant in imported alfalfa or in soil used as ship ballast. Since then, the weed has spread throughout Canada and into almost every state in the United States--and every county in Montana. In late summer and autumn, its one-inch, thistle-like flowers cast a pink-and-lavender hue across dry meadows, pastures, stony hills, roadsides and flood plains. "There are very few species of plant, even invasive ones, that so completely take over a landscape the way that spotted knapweed does," says Callaway. Worse yet, it's tough for native plants to grow back when spotted knapweed has been eliminated. "Many herbicides can kill it easily;" Vivanco says. "The real problem," he speculates, "stems from the fact that spotted knapweed releases a chemical that leaves the soil toxic to the native plants it displaces."

The idea that plants might engage in chemical warfare against each other is even older than spotted knapweed's residence in North America. In 1832, Swiss botanist Alphos-Louis-Pierre-Pyramus DeCandolle speculated that noxious weeds may exude chemicals from their roots that inhibit the growth of other plants. Allelopathy, as the theory is known, has had its ups and downs among scientists; lately, it has been a hypothesis nongrata. Still, Callaway and graduate student Wendy Ridenour decided to see if allelopathy could explain spotted knapweed's success in out competing native plants.

Ridenour grew spotted knapweed together with Idaho rescue, a native bunch grass, in a clear pot filled with sand, enabling her to measure the growth of the plants' roots. Four days after the plants had germinated, rescue roots sharing a pot with knapweed were half the size of those grown alone or with other, native species. Then, when Ridenour spiked the pots with activated charcoal, which absorbs organic chemicals and would neutralize any poison that the weed released, the fescue roots grew at a nearly normal rate despite sharing quarters with spotted knapweed.

Vivanco took on the search for spotted knapweed's chemical arsenal. He and a researcher in his lab, Harsh Bais, found that within two to three weeks of germinating, spotted knapweed seedlings were already churning out a substance that killed any other plant that they exposed to it. The toxin, they found, is a chemical called (-)-catechin (pronounced minus-CAT-e-kin). Most chemicals occur in one of two forms that mirror each other, like left and right hands. Green tea and cotton plant roots produce the "plus" version of catechin, using it as a potent antibiotic to keep bacteria from nibbling on them. But spotted knapweed produces the "minus" form, which almost immediately destroys the roots of other plants. Botanists have long known that plants use chemicals to defend themselves against insects and other predators, says Alastair Fitter, a biologist from the University of York in England. But in this case, the toxin appears to be arming a plant for invasion.

Vivanco and Callaway went on to show that spotted knapweed-infected North American soils had two to three times more (-)-catechin than soils from the plant's native habitat in Europe, where spotted knapweed grows in harmony with thousands of grasses and other perennials. This suggested to the researchers that either European soil microbes had evolved a way of eliminating (-)-catechin or that American spotted knapweed populations produce more of the toxin. The plant's European neighbors are also less sensitive to the chemical; in contrast to their North American counterparts, the native grasses thrived in (-)-catechin soil.

Recognizing that European plants had perhaps evolved a means of coping with the chemical led the scientists to search for North American plants with the same ability. So far, Callaway and Vivanco's groups have found about ten different species that show resistance. Ridenour is now attempting to breed bluebunch wheatgrass, with the goal of producing a native species for replanting efforts.

Another approach is to control the knapweed with natural predators. Jim Story, an entomologist at Montana State University, has gone to Central and Eastern Europe in search of insects that attack spotted knapweed. Through his efforts, some 13 species of beetles, moths and other bugs have been released on spotted knapweed infestations in North America. His current favorite is a Romanian root-boring weevil known as Cyphocleonus achates, a haft-inch-long insect that feeds on spotted knapweed leaves and whose larvae feed on the plant's taproot. Story says extensive testing has been done to try to ensure that none of the spotted knapweed predators has a taste for North American plants.

Yet there's reason to believe that the predator strategy will backfire. Callaway, Vivanco and several colleagues have shown in an unpublished greenhouse study that spotted knapweed responds to some insect attacks by increasing its production of (-)-catechin.

A study of one "natural" insect method of controlling knapweed suggests that the cure may be nearly as bad as the disease. Since the early 1970s, European seed head flies have been released to control spotted knapweed throughout the nation. U.S. Forest Service ecologist Dean Pearson has found that deer mice were gorging themselves on fly larvae inside spotted knapweed flowers. The mice were each eating up to 1,200 larvae per night during the hard Montana winter, getting as much as 85 percent of their diet from them. Deer mouse populations doubled and even tripled in spotted knapweed-infested areas.

The problem is that deer mice are carriers of hantavirus. Since 1993, this highly lethal germ has killed more than 100 people, mostly in the Western United States, with a few cases as far away as Maine and Florida. In the spotted knapweed-infested hills surrounding Missoula, where the European seed head fly is ubiquitous, the number of hantavirus-infected deer mice has skyrocketed. And given that the European seed head fly is now being released in the Eastern United States to control spotted knapweed, it raises the possibility that hantavirus could escalate there as well, says Pearson.

For now, Missoula is attempting to control spotted knapweed on its 4,000 acres of parkland and open space with a 300-strong flock of sheep. "Unlike other grazers, sheep love knapweed, and we're finding they do a pretty good job of controlling the infestation," says Marilyn Marler, Missoula's open space weed coordinator.

Would Wayne Slaght ever think about grazing sheep on the Two Creek Ranch? There's a historic animosity between sheep and cattle ranchers, stemming from range wars in the late 1800s over grazing rights. Perhaps, then, it should come as no surprise that the question triggered a raised eyebrow, a thoughtful look and a quiet shake of the head: "I think I'll wait for something better to come along."

Wicked Weed of the West

Alper, Joe. "Wicked weed of the West." Smithsonian Dec. 2004: 33. Gale. Web. 18 Mar. 2013.

the video

potted knapweed (Centaurea stoebe) is an alien invasive biennial or perennial herbaceous plant. Native to Europe, it is thought to have first arrived in the U.S. in alfalfa in the late 1800’s. It was first reported in the northwest regions of the U.S. Because it can grow under a variety of soil and climatic conditions, it is now found throughout most of the U.S., with concentrations in Montana, Washington, Idaho, and Oregon. There are also major infestations in western Canada. As expected, it is commonly found on disturbed land and along roadways. It is found growing at elevations from 90 feet to 9,000 feet and in areas receiving between 10 to 30 inches of precipitation annually. As with most invasive plants, it easily invades disturbed areas. Unfortunately, spotted knapweed can also invade relatively stable landscapes, making it even more problematic. Unlike some other knapweeds, this plant can invade riparian areas or other areas prone to flooding. Although it has perennial characteristics and can live for up to 9 years, it reproduces primarily from seeds setting up to 1,000 seeds per plant. These seeds can remain viable for many years and can be distributed by wind and animals, and by water flowing in streams.
Economic Impacts of Spotted Knapweed

Spotted knapweed reduces land and forage values since most grazing animals find it undesirable for consumption, although wild and domesticated grazers will eat the plant when other food is not available.
Sheep and goats have been observed readily eating spotted knapweed and are useful as a biological control for the weed.
Current stands or skeletons from past years can impede access to grazing land by livestock and wildlife. Infestations have been reported to decrease grass production on valuable grazing lands by up to 90%, which in turn decreases total nutritional value of available forage.
In 1984, it was estimated that there was a 63% reduction in forage for cattle in Montana due to spotted knapweed. This translates into a loss of about $155.5 million in livestock income if all susceptible lands are invaded.
In British Columbia, the monetary loss in 1979 was estimated at $58 million. These numbers are based on net returns for forage land.
Spotted knapweed infestations have been shown to decrease land values from $40/acre to $26/acre in some areas. These are rough estimates since they are quite difficult and ambiguous to calculate.
Estimated monetary values for wildlife, recreation, and environmental loses are usually harder to estimate. In Montana, recent estimates for losses due to spotted knapweed infestations were set at about $42 million. This includes losses due to decreased economic activity.
More recent estimates for the entire western U.S. for wildlife, recreation, and environmental loses exceed $164.5 million based on infestation area totaling 7 million acres.
On high-value rangeland (based on nutritional and total biomass estimates), control of spotted knapweed is more cost-effective than on marginal grazing land.
There have been some positive uses identified for spotted knapweed. It is a nectar source for some native butterflies and provides nectar and pollen for bees. Extracts from the plant have been shown to have some anti-cancer activity.
For many people, exposure to airborne spotted knapweed pollen can cause seriousallergic reactions including asthma, skin irritation, and hay fever. This is especially problematic in July and August in seriously infested areas.

Ecological Impacts of Spotted knapweed

Spotted knapweed chokes out native plants by out competing them for valuable resources such as space and water.
Spotted knapweed has an allelopathic effect due to chemicals excreted by the plant. For this reason, other plants are unable to germinate and grow near these weeds.
In a survey conducted in 2000, 15% of western wilderness areas reported the presence of spotted knapweed.
Infestations tend to grow at a rate of up to 24% annually. There is concern that much valuable rangeland in the western U.S. is at risk for infestation.
Spotted knapweed infestations can interfere with the production of forage for livestock and wildlife, and with access to available forage. While some wildlife will graze this weed, most herbivores will avoid the plant, perhaps due to bitter chemicals present in the leaves. This tends to influence herbivore distribution and wildlife migration patterns.
Elk seem to be particularly negatively affected by the presence of spotted knapweed because they graze more on the grasses that are displaced by the weed while deer graze primarily on shrubs and trees that are less affected by this knapweed.
Spotted knapweed infestations are known to decrease species diversity by altering rangeland characteristics. The weed out competes native plants for resources, especially when natives are in the critical seedling stage.
Biological diversity is also negatively influenced by changes produced by spotted knapweed infestations.
One of the natural stabilizing factors for rangelands is lichens and mosses that cover exposed soil creating a crust. This crust increases moisture retention and nitrogen fixation. Studies have found that lands infested with spotted knapweed are almost devoid of this protective crust.
In some areas, native species have become endangered or even extinct due to spotted knapweed infestations.
Spotted knapweed increases fire frequency contributing to a decrease in biodiversity. The weed seems to recover from fire more quickly leading to more of the weed and less native plant cover.
Because spotted knapweed has a taproot, it decreases erosion control and soil retention when it replaces native grasses that have fibrous roots. Taproot plants also leave more soil surface exposed and, therefore, increase soil crusting. All of these factors can increase rain runoff and soil erosion.

external image sub3-4_SpottedKnapweedPresc.jpg

tted knapweed is becoming a common weed in Minnesota of roadsides and pastures with dry, sandy soil. Native to Europe and Asia, spotted knapweed was accidentally introduced to North America in the late 1800s. Spotted knapweed can be spread by wind, water, wildlife, vehicles, contaminated hay, farm machinery, gravel distribution, logging equipment, and road construction. Since introduction, this invasive plant has spread to nearly all states in the United States.
Spotted knapweed is a biennial or short lived perennial that grows approximately 2-3 feet tall with gray-green hairy foliage and has pinkish purple flowers. It reproduces quickly by seed and produces a chemical that is toxic to other plants and allows spotted knapweed to displace desirable vegetation. Once established spotted knapweed can become a monoculture and take over large areas. Resulting infestations can reduce forage and wildlife habitat.

2003 LCMR Spotted Knapweed Biological Control Report (PDF: 521 KB)
Assessing the Impacts of Biological Control on Spotted Knapweed in Minnesota (PPT: 14.34 MB)

Spotted knapweed leaf

Spotted knapweed rosette

Spotted knapweed seed

Spotted knapweed seedheads

Biological control is one method to reduce spotted knapweed infestations. Spotted knapweed proliferated in North America unchecked because the insects and diseases that control the plant in its native range were not in North America. The practice of spotted knapweed biological control reunites specialized insects with their host plant, spotted knapweed. These insects were tested extensively to ensure that they will not harm any plants other than knapweeds. The goal of biological control is not to eradicate the weed, but to reduce the infestation to an acceptable level of control.

Biological control agents

In Minnesota, the predominant biological control agents used include seedhead flies, seedhead weevils, and root boring weevils. These three bioagents work in conjunction to control spotted knapweed. Seedhead flies are no longer actively collected and released in Minnesota because they are commonly recovered at infestations making new releases unnecessary. Seedhead weevils and root boring weevils are collected from established sites and released at new sites.

Seedhead flies, Urophora affinis and U. quadrifasiciata

Seedhead flies reduce spotted knapweed seed production and so decrease knapweed spread and proliferation. Adult seedhead flies emerge in the spring, mate and lay their eggs in the developing spotted knapweed flowers. The eggs hatch in 3-4 days and the larvae tunnel into the base of the seedhead. Larval feeding in the seedhead induces the formation of a gall. Most of the larvae will pupate and emerge the following spring. The result of larval feeding is that less seed is available to produce new knapweed plants.

Seed head fly maggots and galls formed in spotted knapweed seedhead

Seedhead fly adult, Urophora affinis

Seedhead fly adult, Urophora quadrifasicata

Seedhead weevils, Larinus minutus and L. obtusus

Seedhead weevils work similarly to seedhead flies in that the eggs are laid on the seedhead and the larvae consume the developing spotted knapweed seed. Adult seedhead weevils overwinter in the plant litter on the ground at the base of spotted knapweed plants. In the late spring and early summer, adults emerge to feed on the foliage, mate and lay their eggs in the knapweed seedhead. The eggs hatch in 3 days and the larvae consume the material in the seedhead for about 4 weeks. Then the adults pupate and emerge to feed on foliage before burrowing in their overwintering sites.

Seedhead weevil adult, Larinus obtusus

Seedhead weevil adults collected in a sweep net, Larinus minutus

Seedhead weevil adult, Larinus obtusus

Seedhead weevil adult, Larinus minutus

Root boring weevils, Cyphocleonus achates

Root boring weevils are highly effective biological control agents because they weaken or kill existing knapweed plants. From mid summer through early fall, adult females lay eggs on the soil surface at the base of knapweed plants. After hatching, the larvae burrow into the roots where they feed and develop over the winter, spring, and early summer. The developing larvae in the roots use precious plant resources and damage the roots. As a result, the plant is weakened or killed. Adults will emerge from the damaged roots in the mid to late summer to feed on the foliage, mate, and start the cycle again.